Government-sponsored school lunch programs have garnered attention from activists and policymakers for their potential to promote public health, sustainable diets, and food sovereignty. However, across country contexts, these programs often fall far short of their transformative potential. It is vital, then, to identify policies and organizing strategies that enable school lunch programs to be redesigned at the national scale. In this article, we use document analysis of historical newspapers and government data to examine the motivating factors and underlying conditions that (...) allowed South Korea’s universal free, eco-friendly school lunch program to become a tool for advancing social justice and ecological goals at the national scale. We analyze the socio-historical evolution and current status of the Korean school lunch program, combining the multi-level perspective with insights from environmental sociology and critical food studies, in order to shed light on the factors that enabled the program to become an innovative niche and articulate the opportunities and challenges it now faces. We identify the state-sponsored creation of what we call “precautionary infrastructure” as a key anchoring mechanism between the school food niche and agri-food regime. Precautionary infrastructure includes new supply chains, certification standards, and sourcing policies that provide a stable market for eco-friendly farms and small-scale producers, while minimizing the environmental health risks of school lunch by delivering organic and pesticide-free ingredients to on-site kitchens that serve free lunches to all students. This analysis offers insight into how public school-lunch programs can become protected niches that help drive sustainability transitions within agri-food systems. (shrink)